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A2 Physics Quantum physics
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- 1Particle modelObjects that have mass and move about according to laws of Newtonian mechanics
- 2Wave modelShaped like a sine graph, do not have mass or charge. Their defining characteristics are diffraction and interference
- 3Photoelectric effectWhen an electromagnetic radiation of sufficiently high frequency falls on a metal surface, electrons are emitted
Delocalised electrons in metal are removed by supplying a small amount of energy provided by the incident electromagnetic radiation
Emitted electrons are called photoelectrons - 4Photoelectric currentCurrent due to photoelectrons
- 5Diagram of photoelectric current
- 61st Law of photoelectric emissionNumber of photoelectrons emitted per second is directly proportional to intensity of incident radiation
- 72nd law of photoelectric emissionMax kinetic energy of photoelectrons is directly proportional to the frequency of the incident radiation but independent of its intensity
- 83rd Law of photoelectric emissionFor every metal, there is a minimum frequency of incident radiation below which photoelectric emission does not take place; threshold frequency
- 9Threshold frequencyMinimum frequency required to release electrons from the surface of a metal
- 10Does the energy of EM waves flow continouslyNo, flows in discrete quanta
- 11PhotonEach quantum of electromagnetic radiation
- 12How to calculate energy of a photon of EM radiationE = hf
h is the Planck's constant - 13Work functionMinimum amount of energy required by an electron to escape its surface
- 14Why electrons are emmited with a range of KEBecuase electrons deeper inside the metal lose energy in collision with atoms as they are emitted
- 15Einstein's photoelectric equationhf = work function + Max E
Meaning energy of the absorbed photon is partly used to release the electron from the metal and partly to give it kinetic energy - 16Wave-particle dualtiyWave behavior: Electromagnetic radiation shows properties of diffraction and interference
Particle behavior: Photoelectric effect - 17Matter waveA moving particle of momentum p will have an associated wave of wavelength where
h = wavelength x p - 18Diffraction of electronsWhen a beam of electrons strikes a thin carbon foil, a diffraction pattern is obtained on a screen
When velocity of electrons in beam was increased by increasing voltage, the rings in the patterns became narrower showing wavelength decreases as velocity increases - 19Ground stateUnder normal conditions, an atom is in its ground state where it posses the minimum possible energy
- 20Excited stateWhen the atom absorbs energy, the energy of the atom increases and the atom is in an excited state
- 21TransitionShifting of electrons between energy levels
- 22How do electrons release energyIn the form of em radiation
The frequencies of em radiation emitted by electrons when they come down to ground state were found to be discrete showing electrons can only absorb certain discrete values therefore energy of an atom is quantized - 23Emission line spectraThe composition of light emitted by a hot gas
The frequencies emitted by atoms a substance when they de-excite from higher to lower energy levels - 24Absorption line spectraWhen white light is passed through a cool gas
The frequencies absorbed from a continuous spectrum by the electrons a substance - 25Line spectra image
- 26Energy level diagrams
- 27Energy bandsAn electron can have an energy at any level in one of the energy bands
However, it cannot have an energy which lies in the forbidden gap - 28Conduction bandIn a metal, the conduction band is only partially filled with free electrons which gives the metal its conductivity
- 29Valence bandIn an insulator, the conduction band is unoccupied and the valence band is fully occupied
- 30Energy bands of conductors and insulators
- 31Metals and energy bandsThe conduction band overlaps with the valence band allowing it to conduct electricity
When a metal is heated, resistance increases because there is no increase in density of electrons in the conducting band; instead, atoms vibrate more and electrons collide more frequently - 32Insulators and energy bandsThere is a large forbidden gap between the valence and conduction band and voltage is insufficient to lift electrons across
- 33Intrinsic semiconductors and energy bandsIts conduction band is also empty however the gap between the two is very small
When heated, electrons gain energy to jump into the conduction band and the material will conduct much better
In an LDR, photons of light are absorbed by electrons in valence bands so they jump the gap into the conduction band
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- AS level Physics Fichas sobre A2 Physics Quantum physics, creado por Sean Byrne el 25/02/2018.
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- Sean Byrne
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